Intermolecular hydroamination of alkynes catalyzed by zinc-exchanged montmorillonite clay

Abstract

Intermolecular hydroamination of phenyl acetylene (PhAc) by aniline to give phenyl-(1-phenylethylidene) amine has been investigated using Zn2+ exchanged K-10 montmorillonite clay (hereafter Zn/K-10) catalysts. Under optimized reaction conditions, aniline to PhAc mole ratio 2, toluene solvent, catalyst Zn/K-10 (0.5 g) and at 130 ◦C gave 77 wt.% conversion of PhAC after 20 h. The activities of Zn/K-10, Zn/H-beta and Zn/silica having same amount of Zn2+ were compared. Zn/H-beta and Zn/K-10 showed nearly the same activity at the end of 10 h and others followed in the order Zn/silica, H-beta, K-10 and silica. The role played by Lewis and Br¨onsted acidities of the catalysts in influencing the catalytic activity for hydroamination reaction has been discussed. It is suggested that Br¨onsted acidity acts as a co-catalyst for Lewis acidic metal center. Zn/K-10 is the inexpensive but efficient catalyst for intermolecular hydroamination of alkynes, which can be utilized as an alternative to Zn/H-beta catalyst.